<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      var year = parseInt(prompt("输入一个数："));
      if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
        document.write(year + "年是闰年");
      } else document.write(year + "年是平年");
    </script>
  </body>
</html>
